Beam, light transmitted

Define Iq to be the intensity of the light incident upon the sample and I to be the intensity of the beam after it has interacted with the sample. The goal of the basic inftared experiment is to determine the intensity ratio I/Iq as a function of the frequency of the light (w). A plot of this ratio versus the frequency is the infrared spectrum. The inftared spectrum is commonly plotted in one of three formats as transmittance, reflectance, or absorbance. If one is measuring the fraction of light transmitted through the sample, this ratio is defined as... 

For transparent plastics materials transparency may be defined as the state permitting perception of objects through or beyond the specimen. It is often assessed as that fraction of the normally incident light transmitted with deviation from the primary beam direction of less than 0.1 degree. 

Fig. 24. The laser beam expander in the Cary 81 spectrometer (exaggerated). Only that part of the expanded plasma light transmitted through the expander is shown.

A significant advance was the application of the Fourier transform technique to enhance the signal. The optical arrangement of a Fourier transform infrared (FUR) spectrometer is shown in Fig. 27.37 (Habib and Bockris, 1984). A beam of light from an IR source is directed to a beamsplitter, where part of the beam is transmitted to a... 

In the double-beam lA-Vis spectrophotometer the light is split into two parallel beams, each of which passes through a cell one cell contains the sample dissolved in solvent and the other cell contains the solvent alone. The detector measures the intensity of the light transmitted through the solvent alone (/q) and compares it to the intensity of light transmitted through the sample cell (/). The absorbance. A, is then calculated from the relationship shown in equation (2.1) ... 

Figure 2.1 Photophysical processes of a beam of light interacting with matter absorption (A), scattering (S), luminescence (L) the rest of the beam is transmitted...

Absorbance and transmittance are two important terms used in absorption measurement. If a beam of radiation of intensity P(> passes through a layer of solution, a part of the light is absorbed by the particles of the solution thus, the power of the beam weakens. The transmittance T of the solution is measured as the fraction of incident light transmitted by the solution. If the intensity of the transmitted light is I then transmittance is measured as,... 

To measure the ultraviolet (or UV-visible) spectrum of a compound, the sample is dissolved in a solvent (often ethanol) that does not absorb above 200 nm. The sample solution is placed in a quartz cell, and some of the solvent is placed in a reference cell. An ultraviolet spectrometer operates by comparing the amount of light transmitted through the sample (the sample beam) with the amount of light in the reference beam. The reference beam passes through the reference cell to compensate for any absorption of light by the cell and the solvent. 

Fig. 7.1. Layout of the infrared spectrometer showing the Michelson Interferometer Optical System. An FTIR spectrometer s optical system requires two mirrors, an infrared light source, an infrared detector and a beamsplitter. The beamsplitter reflects about 50% of an incident light beam and transmits the remaining 50%. One part of this split light beam travels to a moving interferometer mirror, while the other part travels to the interferometer s stationary mirror. Both beams are reflected back to the beamsplitter where they recombine. Half of the recombined light is transmitted to the detector and half is reflected to the infrared source.

Visible and UV absorption spectroscopy are based on studying that part of the incident light transmitted (after absorption) through an electrolytic solution in the same direction as the original beam. However, a certain amount of light is scattered in other directions. 

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